Variable resistor jaw

ABSTRACT

A bipolar forceps for sealing tissue includes an end effector assembly having opposing first and second jaw members each having a proximal end and a distal end. A first electrically conductive surface having two or more conductive sealing plates and a dielectric layer is operably coupled to the first jaw member. Each sealing plate is connected to a reactive element and positioned along the first electrically conductive surface from the proximal end to the distal end. The reactive element of the sealing plate have different impedances. A second electrically conductive surface having one or more conductive sealing plates is operably coupled to the second jaw member. Each electrically conductive surface on the jaw members connects to a source of electrosurgical energy such that the sealing plates are capable of conducting energy through tissue held therebetween to effect a tissue seal.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a Continuation Application claiming thebenefit of and priority to U.S. application Ser. No. 12/176,679 filed onJul. 21, 2008 by Nicole McKenna et al., entitled “VARIABLE RESISTORJAW”, now U.S. Pat. No. 8,469,956 the entire contents of which beingincorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to electrosurgical forceps for assuringuniform sealing of tissue when performing electrosurgical procedures.More particularly, the present disclosure relates to open or endoscopicbipolar electrosurgical forceps that includes reactive elements fordriving different amounts of current through different parts of a jawmember of the forceps in order to get a more controlled distribution ofenergy along the length of the jaw.

2. Description of the Related Art

Forceps utilize mechanical action to constrict, grasp, dissect and/orclamp tissue. Electrosurgical forceps utilize both mechanical clampingaction and electrical energy to effect hemostasis by heating the tissueand blood vessels. By controlling the intensity, frequency and durationof the electrosurgical energy applied through the jaw members to thetissue, the surgeon can coagulate, cauterize and/or seal tissue.

In order to effect a proper seal with larger vessels or thick tissue,many known instruments rely on control of mechanical parameters. Twopredominant mechanical parameters that must be accurately controlled arethe pressure applied to the tissue and the gap distance between theelectrodes. As can be appreciated, both of these parameters are affectedby the thickness of vessels or tissue. More particularly, accurateapplication of pressure is important for several reasons: to reduce thetissue impedance to a low enough value that allows enoughelectrosurgical energy through the tissue; to overcome the forces ofexpansion during tissue heating; and to contribute to the end tissuethickness which is an indication of a good seal.

Even with control over mechanical parameters, however, the tissueportion nearest the pivot of the opposing jaw members tend to receivemore energy delivery than the portions which are distal thereto.Resistance is expressed as resistivity multiplied by, the length dividedby cross-sectional area. The resistance, then, changes as the pressureof the jaws affects the thickness of material held therebetween and thejaw surface area changes. The increased pressure at the distal endsincreases both electrical contact and decreases thickness of tissuethereby requiring, in some instances, a greater amount of energy betweenthe distal ends of the opposing jaw members in order to properly andeffectively seal larger vessels or tissue. Relying on mechanicalparameters alone, without taking into account energy dissipation alongthe length of the jaw, therefore, can lead to an ineffective seal.Energy distribution, if properly controlled, can assure a consistent andreliable tissue seal by compensating for changes in tissue impedancecaused by changes in pressure, surface area, and thickness.

SUMMARY

A bipolar forceps for sealing tissue includes an end effector assemblyhaving opposing first and second jaw members each having a proximal endand a distal end. The jaw members are movable relative to each other inorder to grasp tissue therebetween. An electrically conductive surfacehaving two or more conductive sealing plates and a dielectric layer isoperably coupled to the first jaw member. Each sealing plate isconnected to a reactive element and positioned along the electricallyconductive surface from the proximal end to the distal end. The reactiveelement of the sealing plate positioned on the proximal end of the firstjaw member has a different impedance than the reactive elementpositioned on the distal end. An electrically conductive surface havingone or more conductive sealing plates is operably coupled to the secondjaw member. Each electrically conductive surface on the jaw members isadapted to be connected to a source of electrosurgical energy such thatthe sealing plates are capable of conducting energy through tissue heldtherebetween to effect a tissue seal.

In embodiments, the reactive element is a capacitor, resistor, variableresistor, resistor series, capacitor series, and/or a variable resistornetwork. In embodiments, the dielectric layer is composed of shapememory materials. In embodiments, the bipolar forceps further includes asensor for measuring one or more tissue properties. The sensorconfigures the reactive elements based on one or more tissue propertiesin order to effectively seal tissue. A feedback loop may be used forreal time adjustment of the reactive elements.

The present disclosure also relates to a method of sealing tissueincluding the steps of: providing a bipolar forceps that includes firstand second jaw members each having proximal and distal ends, the firstjaw member having an electrically conductive surface having two or moreconductive sealing plates and a dielectric disposed therebetween. Eachsealing plate is connected to a reactive element and positioned alongthe electrically conductive surface from the proximal end to the distalend. The reactive element on the proximal end has a higher impedancethan the reactive element on the distal end. An electrically conductivesurface is included having one or more conductive sealing platesoperably coupled to the second jaw member. The method also includes thesteps of connecting the jaw members to a source of electrosurgicalenergy; actuating the jaw members to grasp tissue between opposing jawmembers; conducting electrosurgical energy to the electricallyconductive surfaces of the jaw members; and controlling the reactiveelements of the first jaw member to regulate the electrosurgical energyalong the jaw members to effect a tissue seal.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a perspective view of an electrosurgical system including anelectrosurgical forceps and an electrical generator in accordance withan embodiment of the present disclosure;

FIG. 2A is a plan view of the electrically conductive surface of a jawmember in accordance with the present disclosure;

FIG. 2B is a perspective view of an embodiment of the jaw members inaccordance with the present disclosure;

FIG. 2C is a perspective view of another embodiment of the jaw membersin accordance with the present disclosure;

FIG. 2D is a perspective view of yet another embodiment of the jawmembers in accordance with the present disclosure;

FIG. 2E is a plan view of another embodiment of the electricallyconductive surface of a jaw member in accordance with the presentdisclosure;

FIG. 2F is a perspective view of one embodiment of the electricallyconductive surface of a jaw member including stop members in accordancewith the present disclosure;

FIG. 2G is a side view of one embodiment of the electrically conductivesurface of a jaw member including a dielectric layer of varying width inaccordance with the present disclosure;

FIG. 3 is a schematic electrical diagram of the end effector assemblyand generator of the electrosurgical forceps of FIG. 1;

FIG. 4 is a schematic electrical diagram of another embodiment of theend effector assembly and generator in accordance with the presentdisclosure;

FIG. 5 is a schematic electrical diagram of another embodiment of theend effector assembly and generator in accordance with the presentdisclosure;

FIG. 6 is a schematic electrical diagram of another embodiment of theend effector assembly and generator with the resistors arranged inseries in accordance with the present disclosure;

FIG. 7 is a schematic electrical diagram of another embodiment of theend effector assembly and generator of the electrosurgical forceps; and

FIG. 8 is a schematic electrical diagram of a variable resistor whichmay be used with the electrosurgical forceps in accordance with thepresent disclosure.

FIG. 9 is a schematic electrical diagram of an end effector assembly andgenerator having a shape memory switch.

DETAILED DESCRIPTION

Various embodiments of the present disclosure are described hereinbelowwith reference to the accompanying drawings. Well-known functions orconstructions are not described in detail to avoid obscuring the presentdisclosure in unnecessary detail. Those skilled in the art willunderstand that the present disclosure may be adapted for use witheither an endoscopic instrument or an open instrument; however,different electrical and mechanical connections and considerations applyto each particular type of instrument. The novel aspects with respect tovessel and tissue sealing are generally consistent with respect to boththe open and endoscopic designs. In the drawings and in the descriptionwhich follows, the term “proximal”, as is traditional, will refer to theend of the forceps which is closer to the user, while the term “distal”will refer to the end of the forceps which is further from the user.

Referring now to FIG. 1, a bipolar electrosurgical system according tothe present disclosure is shown including electrosurgical forceps 10configured to support end effector assembly 100. Forceps 10 typicallyincludes various conventional features (e.g., a housing 60, a handleassembly 74, a rotating assembly 80, a trigger assembly 70, etc.) thatenable forceps 10 and end effector assembly 100 to mutually cooperate tograsp, seal and, if warranted, divide tissue. Forceps 10 generallyincludes housing 60 and handle assembly 74 that includes moveable handle62 and handle 72 which is integral with housing 60. Handle 62 ismoveable relative to handle 72 to actuate end effector assembly 100 tograsp and treat tissue. Forceps 10 also includes shaft 64 that hasdistal end 68 that mechanically engages end effector assembly 100 andproximal end 69 that mechanically engages housing 60 proximate rotatingassembly 80 disposed at the distal end of housing 60. Rotating assembly80 is mechanically associated with shaft 64. Movement of rotatingassembly 80 imparts similar rotational movement to shaft 64 which, inturn, rotates end effector assembly 100.

End effector assembly 100 includes two jaw members 110 and 120 havingproximal ends 111, 121 and distal ends 113, 123. Jaw members 110 and 120are movable from a first position wherein jaw members 110 and 120 arespaced relative to another, to a second position wherein jaw members 110and 120 are closed and cooperate to grasp tissue therebetween. Each jawmember 110 and 120 includes electrically conductive surface 112 and 122,respectively, disposed on an inner-facing surface thereof. Electricallyconductive surfaces 112 and 122 cooperate to seal tissue heldtherebetween upon the application of electrosurgical energy.Electrically conductive surfaces 112 and 122 are connected to generator20 that communicates electrosurgical energy through the tissue heldtherebetween. A dielectric layer, or insulator substance, 114 may beincluded to limit and/or reduce many of the known undesirable effectsrelated to tissue sealing, e.g., flashover, thermal spread and straycurrent dissipation. By controlling the intensity, frequency andduration of the electrosurgical energy applied to tissue, the tissue canbe selectively sealed.

Generator 20 includes a plurality of outputs for interfacing withvarious electrosurgical instruments (e.g., a monopolar active electrode,return electrode, bipolar electrosurgical forceps, footswitch, etc.).Further, generator 20 includes electronic circuitry configured forgenerating radio frequency power specifically suited for sealing tissue.

Forceps 10 are connected to a source of electrosurgical energy, e.g.,electrosurgical generator 20, via one or more electrical cables.Electrically conductive surfaces 112 and 122, that act as active andreturn electrodes, are connected to the generator 20 through cable 23,which includes the supply and return lines coupled to active and returnterminals 30, 32. Electrosurgical forceps 10 is coupled to generator 20at active and return terminals 30 and 32 (e.g., pins) via plug 92disposed at the end of cable 23, wherein plug 92 includes contacts fromthe supply and return lines. Electrosurgical RF energy is supplied toforceps 10 by generator 20 via a supply line connected to the activeelectrode and returned through a return line connected to the returnelectrode.

Generator 20 includes suitable input controls 25 (e.g., buttons,activators, switches, touch screen, etc.) for controlling the generator20. In addition, generator 20 includes one or more display screens 27for providing the surgeon with variety of output information (e.g.,intensity settings, treatment complete indicators, etc.). The controlsallow the surgeon to adjust power of the RF energy, waveform, and otherparameters to achieve the desired waveform suitable for a particulartask (e.g., coagulating, tissue sealing, division with hemostatic,etc.). Further, forceps 10 may include a plurality of input controlswhich may be redundant with certain input controls 25 of generator 20.Placing the input controls at forceps 10 allows for easier and fastermodification of RF energy parameters during the surgical procedurewithout requiring interaction with generator 20.

When the electrosurgical energy is transferred to the end effectorassembly 100, a sensor, schematically illustrated as 117, may beemployed to determine pre-surgical, concurrent surgical (i.e., duringsurgery), and/or post-surgical conditions. The sensor 117 may be any ofa variety of sensors, such as, for example, a thickness sensor, opticalsensor, or proximal sensor. The sensor 117 may measure tissue propertiessuch as tissue thickness, tissue hydration level, tissue impedance,tissue density, tissue type, and other tissue properties as within thepurview of those skilled in the art. The sensor 117 may also measurestandard electrical parameters such as voltage, current, impedance, andphase. The sensor 117 may be utilized with a closed-loop feedback systemcoupled to the electrosurgical generator to regulate the electrosurgicalenergy based upon one or more pre-surgical, concurrent surgical, or postsurgical conditions. The feedback loop provides real-time adjustment ofthe reactive elements based on the tissue property being measured. It isalso contemplated that forceps 10 and/or electrosurgical generator 20used in connection with forceps 10 may include a sensor 117 or feedbackmechanism which automatically selects the appropriate amount ofelectrosurgical energy to effectively seal the particularly-sized tissuegrasped between jaw members 110 and 120. The sensor 117 or feedbackmechanism may also measure the impedance across the tissue duringsealing and provide an indicator (visual and/or audible) that aneffective seal has been created between jaw members 110 and 120. Varioussensor mechanisms and feedback systems are described in commonly-owned,co-pending U.S. patent application Ser. No. 10/427,832 entitled “METHODAND SYSTEM FOR CONTROLLING OUTPUT OF RF MEDICAL GENERATOR” filed on May1, 2003.

Other electrical connections are positioned through shaft 64 and endeffector assembly 100 to supply bipolar electrical energy to opposingelectrically conductive surfaces 112 and 122 of jaw members 110 and 120,respectively. Forceps 10 also includes a drive assembly (not shown)which imparts movement of jaw members 110 and 120 from the open positionto the clamping or closed position. When electrically conductivesurfaces 112 and 122 of jaw members 110 and 120 are fully compressedabout the tissue, forceps 10 is ready for selective application ofelectrosurgical energy.

The details relating to the inter-cooperative relationships of theinner-working components of forceps 10 are disclosed in commonly-ownedU.S. patent application Ser. No. 11/348,072. Mechanical and cooperativerelationships with respect to the various moving elements of handleassembly 74, rotating assembly 80, and end effector assembly 100 arefurther described by example with respect to commonly-owned U.S. patentapplication Ser. Nos. 10/369,894 and 10/460,926.

Referring now to FIG. 2A, a plan view of electrically conductive surface112 of jaw member 110 is shown. First jaw member 110 includes one ormore sealing plates 116 on electrically conductive surfaces 112. Sealingplates 116 a, 116 b, and 116 c are positioned along electricallyconducting surface 112 from proximal end 111 to distal end 113. Sealingplates 116 a, 116 b, and 116 c each include at least one reactiveelement for effecting the tissue seal. Reactive elements may include acapacitor, resistor, variable resistor, resistor series, capacitorseries, and/or variable resistor network as will be described in detailbelow.

As illustrated in FIGS. 2B-2D, different embodiments are envisioned foraltering the impedance at different locations about first jaw member110. As shown in FIG. 2B, first jaw member 110 includes sealing plates116 a, 116 b, and 116 c disposed about dielectric 114. FIG. 2Cillustrates first jaw member 110 including sealing plates 116 a, 116 b,116 c, and 116 d placed proximal to dielectric 114 which is proximal toelectrically conductive sealing surface 112 which is composed ofelectrically isolated sections 112 a, 112 b, 112 c, and 112 d havingsubstantially the same geometry as the sealing plates. FIG. 2Dillustrates seal plate 116 having a variable width along the length ofjaw member 110 proximal to dielectric 114. Single sealing plate 116provides a smooth change in capacitance along the length of the jaw.Slotted electrically conductive surface 112 allows each electricallyisolated section 112 a, 112 b, 112 c, 112 d, and 112 e to couple tosealing plate 116 independently and spread current.

Sealing plates 116 may be arranged in any configuration conducive toeffectively seal tissue as understood by those skilled in the art.Further, the jaw member may have any number of seal plates in anydesign, such as the jaw member illustrated in FIG. 2E. Sealing plates116 may be composed of metal, such as surgical stainless steel, or otherconducting materials, such as, for example, carbon. Non-conductingmaterial 114 may be an insulating material, such as, for example,polymers including, but not limited to, polyethylene,polytetrafluoroethylene, ethylene propylene diene monomer rubber, andthe like. In a like manner, second jaw member 120 may also have asimilar construction as jaw member 110 described above and include oneor more sealing plates.

In embodiments, at least one stop member 115, as illustrated in FIG. 2F,may be disposed on the inner facing surfaces of electrically conductivesealing surface 112 or 122 to facilitate gripping and manipulation oftissue and to define a gap between opposing jaw members 110 and 120during sealing and/or cutting of tissue. Stop member 115 may extend fromthe sealing surface 122 a predetermined distance according to thespecific material properties (e.g., compressive strength, thermalexpansion, etc.) to yield a consistent and accurate gap distance duringsealing. In embodiments, the gap distance between opposing sealingsurfaces 112 and 122 during sealing ranges from about 0.001 inches toabout 0.006 inches, in other embodiments, from about 0.002 and about0.003 inches. The non-conductive stop members 115 may be part ofdielectric layer 114. Stop member 115 may also be molded onto jawmembers 110 and 120 (e.g., overmolding, injection molding, etc.),stamped onto the jaw members 110 and 120, or deposited (e.g.,deposition) onto the jaw members 110 and 120. For example, one techniqueinvolves thermally spraying a ceramic material onto the surface of jawmembers 110 and 120 to form stop members 115. Several thermal sprayingtechniques are contemplated which involve depositing a broad range ofheat resistant and insulative materials on various surfaces to createstop members 115 for controlling the gap distance between electricallyconductive surfaces 112 and 122.

It is envisioned that a series of stop members 115 may be employed onone or both jaw members 110 and 120 during sealing and/or cutting oftissue. The series of stop members 115 may be employed on one or bothjaw members 110 and 120 depending upon a particular purpose or toachieve a desired result. A detailed discussion of these and otherenvisioned stop members 115 as well as various manufacturing andassembly processes for attaching and/or affixing stop members 115 to theelectrically conductive sealing surfaces 112, 122 are described incommonly-assigned, co-pending U.S. application Ser. No. PCT/US01/11,413entitled “VESSEL SEALER AND DIVIDER WITH NON-CONDUCTIVE STOP MEMBERS” byDycus et al.

FIG. 3 illustrates a schematic diagram of end effector assembly 100 andgenerator 20. Generator 20 provides a source voltage, V_(S), to jawmembers 110 and 120. Disposed between conductive sealing plates 116 and126 of jaw members 110 and 120 is a dielectric, or non-conducting layer,114, thereby forming a capacitor when compressed on tissue having acapacitance between each of the sealing plates 116 (e.g., C₁ and C₂).

The width and thickness of dielectric layer 114 and the surface area ofplates 116 a, 116 b, and 116 c may be adjusted to achieve specificcapacitances, which represent a specific impedance to RF generator 20.Dielectric layer 114 may have a varying thickness across the surfacethereof, such that, for example, dielectric layer 114 is of onethickness around plate 116 a, another thickness around plate 116 b, andyet another thickness around plate 116 c, as illustrated in FIG. 2G. Inembodiments, the dielectric layer 114 may be of varying thickness ormaterial composition across conducting surface 112 or each plate 116,e.g. the carbon amount in filled ethylene propylene diene monomer rubber(EPDM) may be varied along the length of jaw members 110 and 120.

Capacitance and area are calculated based on standard capacitanceformula:

${C\left( {E_{R},A,d} \right)} = \frac{E_{O} \cdot E_{R} \cdot A}{d}$${{Ac}\left( {C,E_{R},d} \right)} = \frac{C \cdot d}{E_{O} \cdot E_{R}}$

wherein:

EO is the absolute permittivity=8.854*10-12 Farad/meter (F/m),

ER is the relative permittivity of the insulation material in (F/m),

A is the surface area of the jaws in meters squared (m2), and

d is the distance between the jaws in meters (m).

The relative permittivity, ER, varies with substance or materialselection, examples of which are given in Table 1:

TABLE 1 Material Relative Permittivity (F/m) Air 1.0Polythene/Polyethylene 2.3 PTFE 2.1 Silicone Rubber 3.1 FR4 Fiberglass4.5 PVC 5.0

The formula to calculate the impedance of a capacitor at the specifiedfrequency C in hertz, is in Farads F:

${R_{C}\left( {C,F} \right)} = \frac{1}{2 \cdot \pi \cdot F \cdot C}$${C_{R}\left( {R,F} \right)} = \frac{1}{2 \cdot \pi \cdot F \cdot R}$

For example, assuming that capacitances, C₁=500 ohms and C₂=1000 ohms,are desired at 472 Khz, and a high dielectric with a relativepermittivity of 5.0 (ER=5.0) and a thickness of 0.5 mm is used. Thesealing plate areas needed are calculated as follow:ER=5.0 d=0.5×10-3 r=500 f=470×10-3AC(Cr(r,f),ER,d)=7.649×10-3 mER=5.0 d=0.5×10-3 r=500 f=470×10-3AC(Cr(r,f),ER,d)=3.825×10-3 mTaking the square root of the area derived, to create a capacitor ofequivalent impedance of 500 ohms at 472 Khz, a sealing plate of 2.77 mm²is required. For the 1000 ohm impedance, a sealing plate of 2 mm² wouldbe used.

By specifically designing the plates 116 and dielectric layer 114 tohave a certain capacitive impedance, the circuit of FIG. 4 can beestablished. Generator 20 generates a source voltage, V_(S). First jaw110 includes three sealing plates 116 a, 116 b, and 116 c separated fromsealing plate 126 of second jaw member 120 via dielectric 114. Sourcevoltage V_(S) is constant and is applied across all three plates 116 a,116 b, and 116 c. Plates 116 a and 116 b, however, include parallelreactive elements R_(a) and R_(b), respectively. R_(a) has a greaterresistance than R_(b) such that with application of a constant voltage,the impedance to the tissue through plates 116 a, 116 b, and 116 cincrease towards the proximal end of jaw members 110 and 120 therebydriving more current through distal end 111. In FIG. 4 and otherembodiments described herein, the reactive elements, R, may be any ofcapacitors, resistors, variable resistors, resistor series, capacitorseries, and/or variable resistor networks to provide the impedanceneeded to control current through the jaws and is therefore not limitedto the particular reactive element exemplified in the embodiments.

End effector assembly 100 may be constructed as shown, or in reverse, sothat jaw member 120 includes more than one plate and associated reactiveelement. In embodiments, such as that shown in FIG. 5, jaw member 110can be split into proximal and distal plates, 116 a and 116 b, connectedby the same wire from voltage source, V_(S), but with increasedimpedance between the wire and the proximal end by use of reactiveelement R_(a) which is greater than R_(b).

In yet other embodiments, such as that shown in FIG. 6, resistors R_(a),R_(b), R_(c), and R_(d) are connected in series across voltage sourceV_(S) thereby forming a voltage divider. The voltage divider may consistof any two or more resistors connected in series across voltage source20. Resistors R_(a), R_(b), R_(c), and R_(d) decrease in resistancealong the length of jaw member 110 towards distal end 113. The sourcevoltage V_(S) must be as high as or higher than any voltage developed bythe voltage divider. As the source voltage is dropped in successivesteps through the series resistors, the source voltage is tapped off tosupply individual voltage requirements to each plate 116. The values ofthe series resistors used are determined by the voltage and currentrequirements of plates 116 a, 116 b, and 116 c as explained above.

In other embodiments, any number of plates may be used with any numberof resistors in any of the configurations described above, such as, forexample, as illustrated in FIG. 7.

In other embodiments, variable resistors may be used. Variable resistor,R_(V), such as that shown in FIG. 8, allows adjustment of the resistancebetween two points, 132 and 134, in the circuit via spindle 136. It isuseful for setting the value of the resistor while in use depending onchanges in other parameters, such as, for example, the distance betweenplates 116, 126.

It is also envisioned that the dielectric 114 may be made of a materialthat expands with temperature, such as shape memory alloys or polymers.Shape memory alloys (SMAs) are a family of alloys having anthropomorphicqualities of memory and trainability and are particularly well suitedfor use with medical instruments. One of the most common SMAs is Nitinolwhich can retain shape memories for two different physicalconfigurations and changes shape as a function of temperature. Recently,other SMAs have been developed based on copper, zinc and aluminum andhave similar shape memory retaining features.

SMAs undergo a crystalline phase transition upon applied temperatureand/or stress variations. A particularly useful attribute of SMAs isthat after it is deformed by temperature/stress, it can completelyrecover its original shape on being returned to the originaltemperature. The ability of an alloy to possess shape memory is a resultof the fact that the alloy undergoes a reversible transformation from anaustenite state to a martensite state with a change in temperature (orstress-induced condition). This transformation is referred to as athermoelastic martensite transformation.

Under normal conditions, the thermoelastic martensite transformationoccurs over a temperature range which varies with the composition of thealloy, itself, and the type of thermal-mechanical processing by which itwas manufactured. In other words, the temperature at which a shape is“memorized” by an SMA is a function of the temperature at which themartensite and austenite crystals form in that particular alloy. Forexample, Nitinol alloys can be fabricated so that the shape memoryeffect will occur over a wide range of temperatures, e.g., −270° to+100° Celsius.

Shape memory polymers (SMPs) may be used instead of, or may augment theuse of, SMAs. SMPs are generally characterized as phase segregatedlinear block co-polymers having a hard segment and a soft segment. Thehard segment is typically crystalline, with a defined melting point, andthe soft segment is typically amorphous, with a defined glass transitiontemperature. In embodiments, however, the hard segment may be amorphousand have a glass transition temperature and the soft segment may becrystalline and have a melting point. The melting point or glasstransition temperature of the soft segment is substantially less thanthe melting point or glass transition temperature of the hard segment.

When the SMP is heated above the melting point of the hard segment thematerial can be shaped. This shape can be memorized by cooling the SMPbelow the melting point of the hard segment. When the shaped SMP iscooled below the glass transition temperature of the soft segment whilethe shape is deformed, a new temporary shape can be set. The originalshape can be recovered by heating the material above the glasstransition temperature of the soft segment but below the melting pointof the hard segment. The recovery of the original shape, which isinduced by an increase in temperature, is called the thermal shapememory effect.

Because capacitance is proportional to the dielectric constant and tothe surface area of the plates and inversely proportional to thedistance between the plates, a dielectric composed of shape memorymaterial that expands with temperature will result in decreasedcapacitance and increased jaw impedance. Thus, a jaw constructed ofshape memory materials will impede RF as the temperature rises.

It is also envisioned, as illustrated in FIG. 9, that a switch may beutilized with the embodiments of the present disclosure. Switch 140 maybe composed of a shape memory material to detect a change in temperatureof current. Switch 140 establishes contact with a correspondingelectrical contact when a particular temperature is reached to allowcurrent to flow therethrough.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A bipolar forceps for sealing tissue, comprising:an end effector assembly having opposing first and second jaw memberseach having a proximal end and a distal end and movable relative to oneanother to grasp tissue therebetween, a first jaw member including: afirst slotted electrically conductive surface including a plurality ofelectrically isolated conductive sections extending across a widththereof; a sealing plate disposed on a center portion of the slottedelectrically conductive surface and having a variable width along alength of the first jaw member thereby providing a varying change incapacitance along the length of the first jaw member; and a secondelectrically conductive surface having at least one conductive sealingplate operably coupled to the second jaw member, wherein the sealingplate and the second electrically conductive surface are adapted toconnect to a source of electrosurgical energy, and wherein impedance isincreased towards a proximal end of the first slotted and secondelectrically conductive surfaces which increases current through adistal end of each of the first slotted and second electricallyconductive surfaces to effectively seal tissue during electricalactivation in a more uniform manner.
 2. The bipolar forceps of claim 1,wherein impedance at each of the electrically isolated conductivesections of the first slotted electrically conductive surface increasestoward the proximal end of the end effector assembly.
 3. The bipolarforceps of claim 1, further including a dielectric layer disposed on aportion of the first slotted electrically conductive surface, thedielectric layer configured to radiate outward from a center portion ofthe first slotted electrically conductive surface.
 4. The bipolarforceps of claim 3, wherein the first slotted electrically conductivesurface has the same geometry as the sealing plate and dielectric layer.5. The bipolar forceps of claim 3, wherein the dielectric layer variesin width along the length of the first jaw member.
 6. The bipolarforceps of claim 1, wherein the first slotted electrically conductivesurface includes stop members that regulate the distance between jawmembers.
 7. The bipolar forceps of claim 1 further comprising: a sensordisposed on one of the first and second jaw members and positioned tomeasure at least one tissue and property relay the measured at least onetissue property to the source of electrosurgical energy to effectivelyseal tissue.
 8. The bipolar forceps of claim 7, wherein the at least onetissue property measured by the sensor includes at least one of tissuethickness, tissue hydration level, tissue impedance, tissue density,tissue type, voltage, current, impedance, and phase.
 9. The bipolarforceps of claim 7, further comprising a feedback loop that providesreal time adjustment of the source of electrosurgical energy based onthe at least one tissue property.
 10. A bipolar forceps for sealingtissue, comprising: an end effector assembly having opposing first andsecond jaw members each having a proximal end and a distal end andmovable relative to one another to grasp tissue therebetween, a firstjaw member including: a first slotted electrically conductive surfaceincluding a plurality of electrically isolated conductive sectionsextending across a width thereof; a sealing plate disposed on the firstslotted electrically conductive surface and having a varying width thatprovides a smooth change in capacitance along a length of the first jawmember; and a second electrically conductive surface having at least oneconductive sealing plate operably coupled to the second jaw member,wherein the sealing plate and the second electrically conductive surfaceare adapted to connect to a source of electrosurgical energy, andwherein impedance is increased towards the proximal end of the firstslotted and second electrically conductive surfaces which increasescurrent through the distal end of each of the first slotted and secondelectrically conductive surfaces to effectively seal tissue duringelectrical activation in a more uniform manner.
 11. The bipolar forcepsof claim 10, wherein impedance at each of the electrically isolatedconductive sections of the first slotted electrically conductive surfaceincreases toward the proximal end of the end effector assembly.
 12. Thebipolar forceps of claim 10, further including a dielectric layerdisposed on a portion of the first slotted electrically conductivesurface, the dielectric layer configured to radiate outward from acenter portion of the first slotted electrically conductive surface. 13.The bipolar forceps of claim 12, wherein the first slotted electricallyconductive surface has the same geometry as the sealing plate anddielectric layer.
 14. The bipolar forceps of claim 12, wherein thedielectric layer varies in width along the length of the first jawmember.
 15. The bipolar forceps of claim 10, wherein the first slottedelectrically conductive surface includes stop members that regulate thedistance between the jaw members.
 16. The bipolar forceps of claim 10,further comprising: a sensor disposed on one of the first and second jawmembers and positioned to measure at least one tissue property and relaythe measured at least one tissue property to the source ofelectrosurgical energy to effectively seal tissue.
 17. The bipolarforceps of claim 16, wherein the at least one tissue property measuredby the sensor includes at least one of tissue thickness, tissuehydration level, tissue impedance, tissue density, tissue type, voltage,current, impedance, and phase.
 18. The bipolar forceps of claim 17,further comprising a feedback loop that provides real time adjustment ofthe source of electrosurgical energy based on the at least one tissueproperty.